This lesson helps introduce students to the concept that temperature causes molecules and atoms to move faster and farther apart, which in turn causes the change from solid to liquid, and liquid to gas.

Population Dynamics

What You Need

Purpose

To help students investigate the causes and consequences of population growth and the environmental factors that contribute to it.

Context

This lesson is part of a group of lessons that focus on the social, behavioral, and economic sciences. These lessons are developed by AAAS and funded by the National Science Foundation Grant No. SES-0549096. For more lessons and activities that take a closer look at the social, behavioral, and economic sciences, be sure to check out the SBE Project page.

In this lesson, students will consider the complex forces that contribute to the growth of the world’s human population. In addition to examining social, ecological, and economic factors, they will focus on the dynamics of change in general and discover the usefulness of graphs in representing it.

Students at these grade levels will benefit from recognizing that the size of the human population and its pattern of growth are influenced by the physical setting and by many aspects of culture: economics, politics, technology, history, and religion. In response to economic concerns, national governments set very different policies—some to reduce population growth, some to increase it. Quite apart from government policy or religious doctrine, many people decide whether to have a child on the basis of practical matters such as the health risk to the mother, the value or cost of a child in economic or social terms, the amount of living space, or a personal feeling of suitability as parents. In some parts of the world—and in poorly educated groups in any country—couples have little knowledge of, or access to, modern birth control information and technology. In the United States, the trend toward casual adolescent sexual relations has led to increasing numbers of unexpected and unwanted pregnancies. (Science for All Americans, pp. 94-95.)

In the course of this lesson, students will begin to consider how social systems are influenced by population growth and how large, gradual increases in the size of a population will require many adjustments, like new government responsibilities, new kinds of institutions, and the need to marshal a more complex distribution of resources. Population patterns, particularly when they are changing, also are influential in changing social priorities. (Science for All Americans, p. 95.)

As they study population dynamics, students may begin to see that social change happens sometimes in a flash, but more often slowly. A point worth raising with students is not whether change is good or bad (it is usually some of each, and in any case different people are apt to judge it differently) or whether it is needed or not (societies need to change over time but they also need stability). What is sought here is an understanding of what kinds of internal and external factors foster social change or influence its character. Another major aim should be to help students to recognize that unless it is imposed by force, social change involves negotiation among different interests—on every level from organizing a neighborhood activity to working out international treaties. Developing such an understanding takes time—time for students to encounter and examine social change in a variety of present and historical contexts. (Benchmarks for Science Literacy, p. 161.)

In the study of constancy and change in this lesson, research suggests that the most important ideas to be dealt with at this grade level are the rates of change and the general notion of evolutionary change. Changing rates need not be calculated but can be identified in graphs and sketched. Especially important is the case in which change rate is proportional to how much there already is (as in population growth). (Benchmarks for Science Literacy, p. 274.)

Motivation

Begin the lesson by writing “Population of the World” on the board with the following timeline provided by About.com: Geography: 1900—1.6 billion; 1950—2.5 billion; 1980—4.4 billion; 2000—6 billion; 2050—?

Have students discuss in small groups what they think the world’s population will be in 2050 and what factors influenced their predictions.

Inform the class at an appropriate time that experts believe the world population will be 9.2 billion by 2050—almost a third more people than there are today.

Questions for them to consider may include:

What do you think daily life might be like in your town in 2050?

What types of technological changes will be needed to accommodate the world’s population growth in 2050?

What do you think will be the greatest environmental concerns at that time?

Do you see population growth becoming a major political issue by 2050? Why or why not? What types of population-related issues might people be talking about at that time?

(Accept all reasonable answers. Encourage groups to elaborate on their responses.)

Development

When they are finished, lead a discussion addressing questions like these:

Why do you think most of the huge growth of the world’s population between 1900 and 2000 (from 1.6 to 6 billion people) occurred after World War II? (Answers will vary. Many people were killed during WWI and WWII, which dominated most of the early part of the 20th century. Improved nutrition and healthcare that came afterward helped people to live longer, while peace and global economic growth also contributed to family and population growth.)

What factors contributed to the doubling of life expectancy during this period? (The agricultural revolution and the availability of antibiotics, vaccines, and pesticides contributed to the increase in life expectancy.)

What does “population momentum” mean? (It means that a large percentage of a population is reaching child-bearing age and that the population is, therefore, likely to increase dramatically.)

What impact does industrialization appear to have on population growth rates? (Statistics show that, as countries become industrialized, women tend to have fewer children. Rates have dropped from nearly 5 births per woman in 1970 to 2.7 births currently.)

What concern does the aging population pose for the governments of many countries? (With increasing proportions of populations growing old and living longer, there will be fewer workers contributing to social security and other similar programs designed to reimburse retired people. Many governments may not have the means to support them.)

Next, divide the class into three groups and make these assignments from the DEPweb, from the World Bank:

Group 1: Read Did You Know?, which covers the effect of income on population growth and representation of change by graphing

Group 2: Read Population momentum, dealing with the influence of age, gender, and urbanization of population growth and representation of change by graphing

Have students read the instructions for their particular group. Remind groups 1 and 2 to click on the hyperlinks for the charts to view them clearly. They also should click to find out more about any of the highlighted terms. Have group 3 click on the four hyperlinks on page 3—GNP per capita, access to safe water, deforestation, and desertification—to learn more about them and their influence on population growth.

Pass out the appropriate Population Growth Group student sheets to each group and have students collaborate on answering the questions on their sheet. (Answers to these questions have been provided on a corresponding teacher answer sheet.) When all the groups have finished, they should be prepared to present a summary of their reading and the answers to their questions to the class. Have students take notes on the other groups’ presentations. Encourage groups to direct others to specific graphs, charts, or maps that support their presentation.

Finally, have the entire class discuss how all the human, social, economic, and environmental variables they have learned about interact and can be made to work together to control population growth.

To check their comprehension and reinforce what they have learned, you also may find it useful to ask the class review questions from the Exercises section at the end of Population Growth Rate: Text Exercises with Answers. Be sure to discuss as a class specific graphs, charts, or maps to give students a greater understanding and opportunity to explore their usefulness in portraying patterns of population growth.

Assessment

Have students write a letter to their congressperson or local newspaper summarizing the problem of population growth and highlighting a specific, realistic action the government or individual citizens can take to help keep earth and its people in balance. Instruct them to include graphs in describing both the problem and its proposed solution.

Extensions

Students may enjoy the Census Bureau’s colorful and informative IDB Population Pyramids (select population pyramid graph from the Select Report dropdown menu), which provide a fun and easy way to visualize population dynamics (in animated pyramid graphs). Users can select any country and track incremental population growth changes based on gender and age up to the year 2050.

Students may enjoy gaining an in-depth understanding of population growth trends in the U.S. by visiting the Census Bureau’s CensusScope. Using current census data and a variety of graphs and maps, CensusScope provides a considerable amount of information and analysis on growth trends based on age, race, households, occupation, and many other factors.

A visit to Sprawl City can help students develop a keener understanding of how population and consumption growth cause cities to grow outward and ultimately destroy surrounding habitats and ecosystems.

SES-0549096
Some of the above content was created with support from the National Science Foundation. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.